Modern metal-wood golf clubs typically include a hollow shaft having a lower end to which the club head is attached. The club head comprises a body and may further comprise a strike plate (also called a face plate) that is attached to the club head body. Club heads also typically are hollow and have thin club head walls. These features have allowed club head volume to increase substantially. But, volume increases are accompanied by an undesirable increase in club head weight unless the mass of material used to make the club head also decreases.
One method for reducing or substantially maintaining mass while increasing volume is to reduce the thickness of the club head wall. For a typical titanium alloy “metal-wood” club head having a volume of 460 cubic centimeters (e.g. a driver) and a crown area of 100 cm2, the thickness of the crown is typically about 0.8 millimeter, and the mass of the crown is about 36 g. Reducing the wall thickness, such as by 0.2 millimeter, would provide a substantial mass reduction.
However, golf club heads having a wall thickness, or some other portion, that is below a certain critical thickness cannot be produced solely by machining or a metal casting process alone. Casting thin walled structures is difficult because it requires forcing material into a corresponding narrow portion of a casting mold before consolidation. Greater force must be applied to urge molten metal fully and completely into the casting mold cavity. Narrower mold cavities and higher pressures increase the probability of turbulent metal flow into the casting mold cavities, which is known to generate casting defects.
Cast golf club components typically are subjected to a finishing process, such as a polishing process, that reduces the thickness of the as-cast article to desired specifications. These mechanical polishing processes must be precisely controlled to produce a final club head having a thickness, particularly in thin cast portions, that is within acceptable tolerances.